Absorption of currents of undesirable frequencies



Jan. 15 1924. 1,480,723

R. E. HELLMUND ABSORPTION OF CURRENTS OF UNDESIRABLE FREQUENCIES Filed Dec. 14 1918 4 Sheets-Sheet 1 L9 ABSORBl/VG MACH/IVE WP NESSES: ENJENTOR fa W HMO/r5. He//muna( ATTOINEY Jan. 15 1924. 1,480,723

R. E. HELLMUND ABSORPTION OF CURRENTS OF UNDESIRABLE] FREQUENCIES Filgd Dec, 14, 1918 4 Sheets-Sheet 2 Hg. 5. E ba/as P INVENTOR WITNESSES:

a 9. W Rude/ff He/Im Una.

ATTORNEY Jan. 15 1924. 1,480,723

R. E. HELLMUND ABSORPTION OF CURRENTS OF UNDESIRABLE FREQUENCIES Filed Dec. 14, 1918 4 Sheets-Sheet 5 Llllllil-LJ WHI'NESSES: I INVENTOR 7Q. Q. l puc/a/fzf //9//munc/.

ATTORNEY Jan. 15 1924. 1,480,723

R. E. HELLMUND ABSORPTION OF CURRENTS OF UNDESIRABLE FREQUENCIES Filed Dec. 14, 1918 4 Sheets-Sheet 4.

Fig.7.

WITNESSES: INVENTOR V Rudolf E. Hellmund.

; ATT'ORNEY Patented Jan. 15, 1924.

UNITED STATES 1,480,723 PATENT OFFICE.

RUDOLF E. HELLMUND, OF SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION 01' PENNSYL- VANIA.

ABSORPTION OF CURRENTS OI UNDESIRABLE FREQUENCIES.

Application filed December 14, 1918. Serial Io. 268,750.

To (all whom it may concern:

Be it known that I, RUooLr E. HELL- .iinxn, a citizen of the German Empire, and a resident of Swissvale, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Absorption of Currents of Undesirable Frequencies, of which the following is a specification.

My invention relates to means for absorbing currents of undesirable frequencies which may exist in the circuits of various types of electrical apparatus. and more particularly in the secondary circuits thereof.

commutator machines of various types are frequently used in the secondary circuits of polyphase induction motors for a number of different purposes such, for instance, as phase-advancement, speed-reguwhich must be handled by the commutator lation, etc. Such machines can be worked quite satisfactorily because the frequencies machine in this instance are usually relatively low.

However, when application of the same principle is attempted in the case of singlephase or unbalanced polyphase induction motors, numerous commutating difiiculties are encountered. These difficulties are principally due to the fact that single-phase induction motors carry higher harmonic currents, in addition to the load currents. of slip frequencies. These currents are usually nearly twice the line frequency (double frequency minus slip) and, in addition, have marked higher harmonics superimposed thereupon. These higher frequency currents are necessary for the satisfactory operation of sin le-phase motors and yet have a very harm ul efi'ect upon the commutation of any commutator machines which may be inserted in the secondary circuit of a singlephase induction motor for purposes, as. above described. It is necessary, therefore,

to allow such hi h harmonic currents to flow in the secon ary circuit of the induction machine and, at the same time, to provide meansfor their elimination from other portions of the electrical circuit.

I propose, therefore, to associate with the secondary circuits of those electrical machines in which higher frequency currents are induced, apparatus which will allow their presence in the required portion of the circuit but, at the same time, will promote the elimination thereof from the circuits of such apparatus as are likely to be harmfully effected thereby.

For a better understanding of my invention reference may be had to the accompanying drawings in which Fig. 1 shows a simple case of a single-phase induction machine in which the undesirable high frequency currents are induced, together with means for eliminating the same; Fig. 2 represents.

two induction machines cascaded and the attendant apparatus for the elimination of the high frequency currents; Fig. 3 is a modification of the system shown in Fig. 2; Fig. 4 illustrates the manner in which the highfre uency current eliminating devices are use with machines such as frequency changers; 5 is a modification of the system shown in Fig. 4 and Figs. 6 and 7 are further modifications in which a negative-impedance is introduced into the eradicator circuit.

Referring now more particularly to Fig. 1, a single-phase induction motor 1, having a single-phase primary winding 2 and a polyp ase secondary. winding 3, is shown as having a regulatin commutator machine 4 in its secondar circuit. Connected between the secon ary winding 3 and the commutator machine 4 is the primary member 5 of an induction machine 15 having a squirrel-cage wound rotor member 7.

In Fig. 2, two induction motors 1 and 8 are shown connected in concatenation. The secondary member 3 of the motor 1 is connected to the primary member 9 of the motor 8 and a secondary member 10 of the motor 8 is connected to the commutator end of a frequency-changer 11, the slip rings 12 of which are connected through a transformer 13 and. a phase-converter 14 of the sin le-phase source of supply, as shown.

small induction machine 15, adapted to have a direct current excitation applied to the secondary member thereof, is connected intermediate the members 3 and 9 and thereby assists in eliminatin any high frequency currents which, whi e they may be necessary for the satisfactory operation of the motor 1, are preferably eliminated from the primary circuit of the motor 8.

I Fig. 3 shows a modification of the system described in connection with Fig. 2, wherein theslip rings 12 of the frequency changer 11 are connected through the transformer 13 directly to the secondary member 3 of the motor 1. In this figure, it will be understood that the motor 8 is of a lower pole number than the motor 1.

In Fig. 4, a frequency-changer 16, having a rotor 17 and a wound stator member 18, is shown as driven by a small commutator machine 19 from any suitable source of power such, for example, as the secondary member 20 of asupply transformer. The frequency-changer 16. is used to furnish reduced frequency to an induction machine 21, this machine here being shown as connected to the commutator end of the frequency-changer 16. The regulating induction machine 15 is, under these circumstances, connected to the stator winding 18 and, by its operation in connection therewith, serves to eliminate] the undesirable high frequency currents.

In Fig. 5, the system of Fig. 1 is modified in so far as the field winding 18 is hereexcited from the commutator end of the frequency-changer; The regulating machine 15 is, therefore, so connected that the currents flowing from the commutator end of the frequency changer may be adjusted'before they pass into the stator winding 18.

In Fig. 6 the harmonic eradicator 15 is .shown as connected to the phase wound member 18 of the frequency changer. By reason of this particular connectionythe field of the frequency changer is freed from such currents as are liable to give rise to undesirable harmonics in the rotor of th regulating machine.

As \a-further eradicating means I have shown in the present case, a negative impedance device 22 inserted between the hereinbefore described eradicating machine 15 and the phase-wound stator member 18. The negative impedance machine 22 is shown somewhat diagrammatically as comprising a rotor having s'hortcircuited brushes and having its field windings connected in series with the stator circuit of the eradicator machine. The insertion of such an additional. impedance device is instrumental in cutting down to a minimum amount the undesirable current which tends to flow.

Having described several modifications of my proposed system for the elimination of undesirable high frequency currents from the machine operating in conjunction with secondaries of electrical machines, the operation thereof is as follows;

Referring to Fig. 1, it is apparent that in order to eliminate from the circuit of the commutator machine 4 those high frequency currents which are induced in the winding 3, it will be necessary to provide a shunt circuit through which such high frequency currents may flowwithout undue obstruction. This means isprovided by running the machine 15 at a speed corresponding to the synchronous s eed of the slip frequency of the motor 1. the winding 5 will constitute a very high impedance for currents of the slip frequency.

provided with the necessary high frequency currents for satisfactory operation and, at the same time, serves to-eliminate from the primary winding '9 such undesirable frequency currents.

In Fig. 3, the method of connecting the h slip rings of the frequency-changer directly to the intermediate circuit serves to furnish the excess power derived from this frequency changer to the intermediate circuit. This connection is particularly advantageous when two motors of different current capacity or pole numbers are cascaded. If,

nder these. circumstances,

for example, we consider the motor 8 to have four poles while the motor 1 has eight poles, which, of course, means larger cur- ,rent capacity for the four-pole connection when the motors are of equal size, a greater total output may be obtained if the primary member 9 of the motor 8 is furnished with the additional power derived from the frequency changer, as shown in the connections of this figure. Moreover, it is quite possible to obtain satisfactory operation and elimination of undesirable currents under these circumstances without the use/of the absorbing machine 15.

In Fig. 4, the output voltages of the frequency-changer 16 usually contain higher harmonics on account of the fact that the field of the machine is not a rotating field of uniform strength. This field may, however, be smoothed out and the desired char-' impedance devices shown are preferably inserted to obtain satisfactory're lation.

The operation of thes stem si ewn 'n Fig. 6 is analogous to that escribed in connection with the system shown in Figs. 4 and 5 with the exception that the additional impedance device gives slightly more satisfactory results under some conditions of opera; tion. When used as described in connection with the above system the eradicator may be furnished with a direct-current excited field and is, therefore, able to furnish an out-of-phase component of electromotive force to the system which operates to greatly improve the power factor of the line. In all cases of this kind, the relative effect of the eradicator is better if its resistance and leakage reactance is small, compared to the resistance and leakage reactance of the mo tor controlled by the regulating frequency changer. The proper relation can, of course, be obtained by the proper design of the two machines, but can be improved, or even secured altogether, by means of external devices such as the negative impedance booster 22 in series with the absorbing machine 15, or the impedance or reactance devices 23 in series with the load machine 21.

In all of the above described systems, it should be borne in mind that the eradicator machine should follow in general the design indicated in connection with Fig. 6, that is, it should have low resistance as well as low leakage reactance. Thus, in Fig. 7 is shown a combination similar to that shown in Fig. 3, but with the addition of a polyphase commutator-type booster 22* in series with the machine 15, and a plurality of im edance devices 23 in series with the windings 9. Moreover, it is, of course, entirely possible to supply any of the eradicator machines shown in the above system with direct current excited fields, thereby obtaining a greater degree of harmonic eradication under some circumstances. I

While I have shown several systems for the elimination of undesirable high frequency currents in connection with electrical machines of the class described, it is entirely possible that many modifications thereof may occur to those skilled in the art, and I desire, therefore, that only such limitations be placed on my invention as are imposed by the scope of the prior art or specifically set forth in the appended claims.

I claim as my invention:

1. The combination with a dynamo-electric machine having primary and secondary circuits, said secondary circuit carrying currents of a plurality of frequencies, of an electrical energy-translating device connected to said secondary circuit and requiring currents of only one of said frequencies, and a shunting means connected to said secondary circuit to absorb substantially all of the currents of the other frequencies while drawing substantially no current of said required frequency.

2. The combination with a dynamo-electric machine havin primary and secondary circuits, said secon ary circuit carrying currents of a plurality of fre uencies, of means connected to said secon ary circuit and furnishing a negligibl small conductance to currents of one of sai frequencies but being substantially a short circu1t for currents of the other frequencies.

3. The combination with a dynamo-electric machine havin primary and secondary circuits. said secondary circuit carrying currents of a plurality of frequencies, of an electrical energy-translating device connected to said secondary circuits and requiring currents of only one of said frequencies, and a freely running dynamo-electric machine connected in shunt with said device and adapted to absorb currents of the other frequencies.

4. The combination with a dynamo-electric machine having primary and secondary circuits, said secondary circuits carrying currents of a plurality of frequencies, of an electrical energy-translating device connected to said secondary circuit and requiring currents of onlyone of said frequencies and a freely running induction machine having a primary winding connected in shunt with said device and having a good damper winding whereby said induction machine is adapted to absorb currents of the other frequencies.

5. The combination with a dynamo-electric machine having primary and secondary circuits, said secondary circuit carrying currents of a plurality of frequencies, of an electrical energy-translating device connected to said secondary circuit and requiring currents of only one of said frequencies and an induction machine having its primary connected to said secondary circuit, said induction machine offering a negligibly small conductance to currents of said frequency,

but constituting a shunt path of negligibly low impedance for currents of the other frequencies.

6. The combination with two cascaded induction motors adapted to be supplied from a single-phase source, of a frequency changer having one end connected to the secondary member of the second motor and having its other end connected to the intermediate circiut between said motors, and dynamo-electric means connected across said intermediate circuit to selectively absorb currents of frequencies other than those required to operate said second motor.

7. The combination with a dynamo-electric machine having primary and secondary circuits said secondary circuit carrying cur rents of a plurality of frequencies, of an induction machine having its primary connected to said secondary circuit, said induction machine o'liermg a negligibly small condnctance to currents of one of said frequencies but constituting a path of substantially low impedance for currents of the other frequencies.

8. The combination as set forth in claim 7, in. combination with a dynamo-electric machine operating as a booster to reduce the impedance of the induction machine circuit to currents flowing therein.

9. The combination with a dynamo-electric machine having primary and secondary circuits, said secondary circuit carrying currents of a plurality of frequencies, of a second dynamo-electric machine connected to said secondary circuit and requiring currents of only one of said frequencies, and an auxiliary induction machine having its primary connected to said secondary circuit, said auxiliary machine offering a negligibly small conductance to currents of said frequency, but constituting a shunt path of substantially low impedance for currents of the other frequencies.

10. The combination as specified in claim 9, characterized by the fact that the reacta-nce due to the resistance and leakage of the auxiliary machine is small compared with the corresponding reactance of the Second dynamo-electrio machine.

11. The combination as specified in claim 9, in combination with means external of said machines for, in effect, increasing the relative leakage flux of said second dynamoelectric machine as compared with the auxiliary induction machine.

12. The combination as specified in claim 11, said external means comprising a series, commutator, polyphase booster 'in'series circuit relationship with said auxiliary induction machine.

13. The combination with a dynamo-electric machine having primary and secondary circuits, said secondary circuit carrying fundamental and harmonic currents, of an electrical energy-translating device connected toflsaid seeondary current and requiring said,'.=finrdamental currents only, and an inducti machine having its primary; connented to "dfseco'ndary circuit, said induction- '6, nc ofie'ring anegligibly small conduct aidfundamental currents butcon .shunt path "of substantially jl'o' e 5 for said h armonic currents.

l b-The y 13,"in conib tio ii;as specified in claim r ithmeans external of said electrical; e and said induction machine for'increasing the relative value of the admittancenofrs'aid induction, machine to said harmonic currents-as compared with the admittance 'of said electrical device to said harmonic currents.

In testimony: whereof, have hereunto subscribed my name this 4th day of Dec, 1918.

R noLr E. HELLMUND. 

